Electrical Design
Summary
The Electrical Design document defines the electronic components, circuits, and electrical specifications of your medical device. This document covers component selection, circuit schematics, PCB layouts, power requirements, and electrical safety measures essential for safe and reliable device operation.
Why is Electrical Design important?
Electrical design documentation is critical for patient safety because electrical components can pose risks of shock, fire, or electromagnetic interference that directly affect patient care. Poor electrical design can lead to device malfunction, safety hazards, or electromagnetic compatibility issues that compromise device performance. Regulatory authorities require detailed electrical specifications to ensure devices meet safety standards and perform reliably in medical environments.
The electrical design also demonstrates that you have systematically considered electrical safety, power management, and electromagnetic compatibility. This documentation supports risk management, safety testing, and verification activities throughout the development process.
Regulatory Context
Under 21 CFR Part 820.30 (Design Controls) and IEC 60601 Part 1 (Medical Electrical Equipment):
- Electrical specifications must be documented as design inputs
- Electrical safety requirements per IEC 60601 Part 1 series standards
- Electromagnetic compatibility per IEC 60601 Part 1-2
- Risk management for electrical hazards per ISO 14971
Special attention required for:
- Electrical safety testing (leakage current, dielectric strength, grounding)
- EMC testing for electromagnetic compatibility
- Power supply safety and efficiency requirements
- Cybersecurity considerations for connected devices
Under 21 CFR Part 820.30 (Design Controls) and IEC 60601 Part 1 (Medical Electrical Equipment):
- Electrical specifications must be documented as design inputs
- Electrical safety requirements per IEC 60601 Part 1 series standards
- Electromagnetic compatibility per IEC 60601 Part 1-2
- Risk management for electrical hazards per ISO 14971
Special attention required for:
- Electrical safety testing (leakage current, dielectric strength, grounding)
- EMC testing for electromagnetic compatibility
- Power supply safety and efficiency requirements
- Cybersecurity considerations for connected devices
Under EU MDR 2017/745 and General Safety and Performance Requirements:
- Electrical design must comply with Essential Requirements Annex I
- Electrical safety per IEC 60601 Part 1 and harmonized standards
- EMC compliance per IEC 60601 Part 1-2 for medical environments
- Risk management for electrical hazards per EN ISO 14971
Special attention required for:
- CE marking requirements for electrical safety and EMC
- Harmonized standards compliance (IEC 60601 series)
- Electrical safety documentation for notified body review
- Energy efficiency requirements where applicable
Guide
Understanding Electrical Design
Electrical design encompasses all electronic aspects of your medical device that handle power, signals, or data processing. This includes:
- Power Systems: Batteries, power supplies, charging circuits, and power management
- Signal Processing: Amplifiers, filters, analog-to-digital converters, and sensors
- Control Circuits: Microcontrollers, processors, memory, and control logic
- Communication Interfaces: Wireless modules, USB, Ethernet, and data transmission
- Safety Circuits: Isolation, protection, monitoring, and fail-safe mechanisms
Component Selection and Specifications
Document each electrical component systematically:
- Component List: Identify all electrical parts with manufacturer part numbers
- Electrical Specifications: Voltage, current, power, frequency, and tolerance requirements
- Environmental Ratings: Operating temperature, humidity, and vibration specifications
- Safety Certifications: UL, CE, or other safety approvals for critical components
- Supply Chain Information: Primary and backup suppliers for critical components
Circuit Design and Schematics
Your electrical design documentation should include:
- System Block Diagrams: High-level functional blocks and signal flow
- Detailed Schematics: Complete circuit diagrams with component values
- Power Distribution: Power supply design and distribution networks
- Signal Integrity: Impedance control, noise reduction, and signal routing
- Protection Circuits: Overcurrent, overvoltage, and ESD protection
PCB Layout and Assembly
Document the physical implementation:
- PCB Stack-up: Layer count, thickness, and material specifications
- Component Placement: Critical component positioning and thermal considerations
- Routing Guidelines: Trace width, spacing, and impedance requirements
- Manufacturing Specifications: Drill sizes, solder mask, and silkscreen requirements
- Assembly Instructions: Pick-and-place files and soldering specifications
Electrical Safety Requirements
Your electrical design must address:
- Isolation Requirements: Patient isolation per IEC 60601 Part 1 standards
- Leakage Current: Limits for patient and earth leakage currents
- Protective Earth: Grounding and bonding requirements for safety
- Fault Conditions: Single fault safety and redundancy requirements
- Environmental Protection: Ingress protection (IP) ratings for enclosures
Electromagnetic Compatibility (EMC)
Design for EMC compliance:
- Emission Control: Limiting electromagnetic emissions per CISPR standards
- Immunity Requirements: Resistance to electromagnetic interference
- Shielding Design: Enclosure shielding and cable shielding requirements
- Filtering: Power line filters and signal filters for noise reduction
- Layout Considerations: PCB layout techniques for EMC compliance
Example
Scenario: You’re developing a wearable heart rate monitor that continuously measures ECG signals and transmits data wirelessly to a smartphone app. Your electrical design must ensure patient safety, signal accuracy, and reliable wireless communication.
Electrical Component Specifications
| Component | Part Number | Manufacturer | Specifications | Function |
|---|---|---|---|---|
| ECG AFE | ADS1293 | Texas Instruments | 3-channel, 24-bit ADC, 125 SPS | ECG signal acquisition |
| Microcontroller | nRF52840 | Nordic Semiconductor | ARM Cortex-M4, Bluetooth 5.0, 1MB Flash | Signal processing and wireless communication |
| Battery | ICR18650-26F | Samsung SDI | 3.7V, 2600mAh, Li-ion | Power supply |
| Charging IC | BQ24040 | Texas Instruments | 1A, USB charging, thermal regulation | Battery charging management |
| Accelerometer | LSM6DS3 | STMicroelectronics | 3-axis, +/-16g, I2C interface | Motion detection and artifact removal |
| Crystal Oscillator | FC-135 | Epson | 32.768 kHz, +/-20 ppm | Real-time clock reference |
Circuit Design Specifications
Power Supply Design: 3.7V Li-ion battery with 3.3V and 1.8V regulated outputs using low-dropout regulators. Power consumption optimized for 7-day battery life with continuous monitoring.
ECG Signal Chain: Differential input with 40dB gain, 0.5-100 Hz bandpass filtering, and right-leg drive for common-mode rejection. Input impedance >10 GOhm to minimize electrode artifacts.
Wireless Communication: Bluetooth Low Energy 5.0 with -20 dBm to +8 dBm transmit power. Antenna design optimized for body-worn applications with SAR compliance.
Electrical Safety Implementation
Patient Isolation: Reinforced isolation between patient-connected ECG inputs and all other circuits per IEC 60601 Part 1. Isolation barrier rated for 4000V AC.
Leakage Current: Patient leakage current <10 microA under normal conditions and <50 microA under single fault conditions. Earth leakage current <500 microA.
Protection Circuits: ESD protection on all patient-connected inputs rated for +/-15 kV air discharge. Overcurrent protection on battery charging circuit.
PCB Design Requirements
4-Layer PCB Stack-up: Signal/Ground/Power/Signal with 1.6mm total thickness. FR-4 material with controlled impedance for high-speed signals.
Component Placement: ECG analog front-end isolated from digital switching circuits. Crystal oscillator placed close to microcontroller with guard traces.
EMC Considerations: Continuous ground plane, proper via stitching, and ferrite beads on power supplies. Bluetooth antenna keepout zones maintained.
Testing and Verification
Electrical Safety Testing: IEC 60601 Part 1 compliance testing including leakage current, dielectric strength, and protective earth resistance.
EMC Testing: IEC 60601 Part 1-2 compliance for emissions and immunity in medical environments.
Performance Testing: ECG signal accuracy verification, wireless range testing, and battery life validation under various usage scenarios.